Severe packet loss (over WiFi)

Since about two weeks ago, usually after one or two days uptime, I observe sudden and gradually worse and worse packetloss 10-100% for wifi clients, in the end it’s not even possible to log in. (I do not have Ethernet clients on this one).
There are no signs of resource overload in the box*
Apart from resetting the box, killing all the /usr/bin/foris-controller processes resolves the problem as well.
This has happened to me about 6 times already.

This is with the blue Turris 1.X
foris version: 100.5

Device Turris
Serial number censored
Turris OS version 3.11.16
Kernel version 4.4.199-f90a52a6230ecb072f657fce5aebd444-0

Is this a known issue?

TIA
P.

Mem: 316612K used, 1754864K free, 1744K shrd, 0K buff, 166624K cached
CPU: 0% usr 0% sys 0% nic 98% idle 0% io 0% irq 0% sirq
Load average: 0.03 0.02 0.06 3/111 14046

It’s not good idea to public share of your router SN.

correction: killing foris-controller processes does not have an effect, it must’ve been a coincidence earlier.

Are you using 2.4 GHz frequency or 5 GHz?

2.4 GHz, Mode n, WPA2 PSK
There are no other WiFi networks on the same or adjacent channel

I’ve downgraded the system to 3.11.13 and the issue is still present. I guess this points to a hardware problem, but I’ll try to restore to factory default when I have some time to be sure.